1. Field of the Invention
This invention relates to the remediation of ponds and other sites which contain sludge and, in particular, to an economic and efficient process for dredging and dewatering the sludge to produce a solid sludge material which can be disposed of in an environmentally safe manner and/or further treated to recover metals and other valuable materials in the sludge before disposal.
2. Description of Related Art
One of the most important global problems is the protection of the environment. Solutions are needed for our environmental problems from both a preventive stand point and the clean-up of existing environmental hazards.
Government and industry have recognized these problems and have adopted over the years a number of environmental safety measures to minimize the discharge of wastes and toxic materials into the environment. One approach is the use of ponds to contain waste streams which may then be treated and disposed of in an environmentally safe manner. The remediation of water containing polluted sites including waste process ponds at industrial sites and other water sites where sediment, sludge and other wastes including hazardous and toxic materials have accumulated is the next step for the safe removal and disposal of these polluting materials.
Remediation is basically the process of removing wastes and hazardous materials from a site and returning of the site to its original condition. Typically, industrial ponds and other water sites containing waste materials produce a sludge or silt at the bottom of the pond which contains the bulk of the potentially polluting and toxic material in the pond and this material must not only be removed so that the pond is remediated but also the sludge must be disposed of in an environmentally acceptable manner.
The remediation of ponds and other water sites containing waste materials is generally accomplished by conventional dredging and dewatering systems employing a multi-step process. Firstly, pond bottom sludge is removed and pumped to onshore equipment where the sludge is then screened for removal of oversized material such as rocks, bricks and other debris. The screened sludge (also termed "sludge underflow") which contains most of the sludge is pumped directly to a filter press feed tank from which the sludge is pumped to a filter press for dewatering. A polymer is usually added to the sludge stream at the filter press inlet to aid in dewatering. Pressed and dewatered sludge, now in cake form, is transferred to a disposal site or storage area.
Dredging is basically marine excavation whereby a dredge mounted on a barge or boat removes the sludge from the site. There are two basic types of hydraulic dredges, one being the clamshell or bucket and the other being a suction dredge. The suction dredge uses a movable suction pipe which is lowered to the bottom of the site and which often has a rotating cutter head at the bottom end. The cutter churns up the bottom and pumps on the barge or boat or at the cutter suck up the water and sludge suspended in it and transport the sludge to land for dewatering.
While conventional dredging and dewatering processes are adequate for many remediation projects, improvement is needed in the process to provide a more efficient and effective process employing a relatively small amount of low cost commercially available equipment yet still providing high production (remediation) rates and greater control of the process. One aspect of the efficiency of the process is the need to provide substantially clear process water return to the pond being remediated. An additional aspect of the improved process is to provide a thickened even sludge feed to the press which increases press production and can produce a sludge cake drier than sludge cakes produced in conventional remediation processes.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a remediation process for ponds and other water sites containing waste materials which is efficient and economic and which has high production (remediation) rates.
Other objects and advantages will be readily apparent from the following description.